Soluble coffee, although a very popular product, suffers the disadvantage that it does not have the appearance of coffee particles obtained by the grinding of roasted coffee beans. Soluble coffee granules are usually of a reasonably uniform, rounded shape while roast and ground coffee particles usually appear to have various shapes; often sharp. Also, the color of soluble coffee is lighter and more uniform than the color of roast and ground coffee. In particular, typical roast and ground coffee is reasonably dark in color but contains a noticeable fraction of larger, lighter colored material which gives it a speckled appearance. For example, when measured on an Agtron colorimeter, roast and ground coffee particles usually have a color in the range of 60 to 65 Agtron units while soluble coffee particles have a color in the range of 75 to 90 Agtron units; which is much lighter. The particle size distribution of soluble coffee is also different from that of roast and ground coffee. Further, the bulk densities of soluble coffee granules and roast and ground coffee particles also differ.
However, it has been long appreciated that a soluble coffee product which better simulates the appearance of roast and ground coffee particles is likely to be much more acceptable to the consumer. The reason is that consumers often associate a product, which has the appearance of roast and ground coffee, with quality. Consequently there have been many attempts to alter the appearance of soluble coffee so that it better simulates that of roast and ground coffee. Unfortunately, this has proved to be difficult since many of the characteristics of soluble coffee are interrelated and hence altering one to produce a beneficial effect often results in an adverse effect in another characteristic. Also, many constraints exist; for example the bulk density of the product should be such that a teaspoon of the product yields an acceptable cup of coffee. Altering the size distribution or using processes to alter the color can result in unacceptable changes to the bulk density.
One of the earlier attempts to provide a product which better approximates the appearance of roast and ground coffee is described in U.S. Pat. No. 3,821,429. Here a first portion of darker coffee granules is produced by spray drying a coffee extract. Then a lighter portion is produced by freeze drying a coffee extract under selected conditions to provide a product which has a color of at least 5 Hunter L scale units less than the dark portion. The two portions are then mixed in the amount of 10% to 50% light portion to 90% to 50% dark portion. An agglomerating fluid is then distributed over the mixture to cause the granules to become tacky and adhere to other granules. The mixture is meanwhile agitated until at least 80% of the particles have a size in the range of 12 to 48 US standard mesh (about 1.41 mm to 0.297 mm). If necessary the product is dried and packed. The process is complicated in that both spray dried and freeze dried coffee is used. Also the process does not address many of the characteristics of soluble coffee granules which differ from roast and ground coffee.
Another early attempt is disclosed in U.S. Pat. No. 3,493,388. In this process, spray dried particles passing through a 16 US standard mesh (about 1 mm) are first produced. The particles are then chilled and ground to pass through a much finer screen, for example a 100 US standard mesh (about 149 microns). The particles are then agglomerated in a steam agglomerator under specific conditions and dried. Agglomerates which are too fine or too coarse are removed and recycled. The agglomerate obtained is dark. Simultaneously, a lighter colored , freeze dried product of reasonably similar particle size distribution is prepared. The freeze dried product however has a lower moisture content than the spray dried product. The two products are then mixed with the mixture containing more darker agglomerates than lighter agglomerates. The product is said to have a speckled appearance and the two portions are said not to separate during storage since, due to the difference in moisture content, the agglomerates cling to one another. However the process is again complicated in that both spray dried and freeze dried coffee is used. Also again the process does not address many of the characteristics of soluble coffee granules which differ from roast and ground coffee.
A process which attempts to provide a product which has the appearance of roast and ground coffee but which has an acceptable bulk density is described in U.S. Pat. No. 4,594,256. Here spray dried coffee granules are milled to produce a powder of an average particle size of 25 to 75 microns. Then the cohesiveness of the powder is adjusted so that the particles have a cohesion index of 0.20 to 0.85. In this way, the particles bind together to form loosely packed clusters which will hold together during further processing. The clusters are vibrated and screened to give granules of regular shape and size in the range of 800 to 2100 microns. The granules are then subjected to steam agglomeration to produce agglomerates having a dark color. The granules have a density of 0.20 to 0.28 g/cm.sup.3 and about 5% of the surface of the granules have a lighter color due to imperfect darkening. Processes deviating in minor aspects from this process are disclosed in U.S. Pat. Nos. 4,594,257 and 4,594,258. However again in all cases, not all characteristics of soluble coffee granules which differ from roast and ground coffee are addressed.
A darkening process which produces particles of different shapes, particularly shapes with sharp edges, is disclosed in U.S. Pat. No. 4,640,839. In most of the prior processes, the particles produced have smooth, rounded edges and a sponge-like texture very dissimilar to roast and ground coffee particles. In the process disclosed in U.S. Pat. No. 4,640,839, spray or freeze dried coffee powder is allowed to fall in a stream through a cloud of steam. The steam causes the surface of the particles to form a flowable phase, which may result in some agglomeration of particles. The particles are then dried. The dried particles have a speckled appearance and have irregular shapes with sharp edges. By varying the time spent in the steam cloud, the darkness of the product can be varied. Hence darker and lighter products can then be mixed. Although the process usefully produces particles of the required shapes and densities, there is no specific teaching on how to obtain certain other desired characteristics.
Therefore there is still a need for a relatively simple and economically viable process for producing a soluble coffee product which closely simulates the appearance of roast and ground coffee particles.